1. Field of the Invention
This invention relates to support devices to maintain the spine in a suitable position for spinal surgery.
2. Prior Art
During orthopedic surgery, when the lumbar spine is to be operated on, the patient must be placed in a position which takes pressure off the chest cavity and abdomen. Presently, there are three conventional positions in which a patient may be placed during surgery. In the first, or "prone position", the patient is placed face down over bolsters on the operating table. The degree of exposure of the spine is well controlled, however, the abdomen and chest often become depressed. This thoracic (chest) compression often interferes with proper ventilation of the anesthetized patient and increases the resistance to return of venous blood to the heart. Furthermore, the abdominal compression may produce transmitted compression of the inferior vena cava which may cause engorgement of the epidural veins. As a result, the patient will have a tendency to bleed which presents a serious obstacle to the surgeon as landmarks are obscured, operating time prolonged, and vital structures are endangered. Also blood loss may pose a life threatening situation which makes demands on the surgeon and compromises the extent of the proposed surgery.
In the second, or "lateral recumbent position," the patient respirates freely and the venous return is not blocked. However, in this position, spinal fusion to the tips of the transverse processes is difficult.
In the third and position, the "knee-chest position," the lumbar spine is flexed and the interlaminar spaces in the spinal column are opened widely. In this position, the patient's respiration is satisfactory and no pressure is exerted on the inferior vena cava. However, flexing the interlaminar spaces does tend to increase tension on nerve roots which have already been quite tight due to disc herniation. The full flexion of both hips and knees is required and may impede venous return from the legs, produce stasis and causes deep-vein thrombosis. Furthermore, in this position, the patient is often unstable and is prone to motion during surgery. The knee chest position can be improved as to enhance the benfits of the position while decreasing its liabilites. This produces the so called modified knee-chest position where the knees are not actually against the chest but rather bent to a right angle with the hips similarly bent to a right angle. A special frame is required to maintain a patient in this modified knee-chest position.
One such device was developed by Hastings and is disclosed in an article in the Canadian Journal of Surgery, pages 251-253, volume 12, April 1969. Hastings discloses a wooden frame having an adjustable seat and a removable cross bar extending across the frame to add stability. The frame is attached to a standard operating table by a standard metal mount which rests on the operating table. The degree of flexion or extension of the lumbar spine is controlled by changing the height of the rest that supports the patient's chest.
A problem encountered in using this particular frame is that the height and location of the frame cannot be adjusted to accommodate patients of various sizes and shapes. For example, if the patient is to be fused in extension, a higher frame must be selected rather than adjusting the height of the frame. Furthermore, since the frame is comprised of wood, it exposes a rough surface that can cause injury to the patient, due to splintering and absorption of blood in the wood material. Also, because the seating platform is adjustable, it has a tendency to slide under the weight of a heavy patient, causing the patient to move out of proper position and thereby making the surgical process more difficult and time consuming.